1. Field of the Invention
The present invention relates to a screen printing method, and more specifically to a screen printing method in which screen printing is carried out by placing a material to be printed on a printing table at a predetermined portion, feeding a coating material in a paste state or an ink state onto the surface of a screen plate for printing, and sliding a squeegee on the surface of the screen plate.
2. Prior Art
In screen printing, a desired printing has been carried out on a printing surface of a material to be printed by placing the material to be printed on a predetermined portion of a printing table, and feeding a paste-state or ink-state coating material comprising an insulating material or a dielectric material onto the surface of a screen plate for printing using a squeegee or a squeegee and a scraper.
The conventional screen printing method has been usually carried out under atmospheric pressure. Screen printing using a stencil made of a metal, and screen printing using a screen plate made of a gauze-adhered plate are known. In the former screen printing using a stencil made of a metal, the stencil is contacted to a printing surface of a material to be printed, and printing is carried out by pouring the paste-state or ink-state coating material into pore portions of the stencil. Thus, printing is carried out by a squeegee without coating by using a scraper.
Also, in the latter screen printing using a screen plate comprising a gauze-adhered plate, printing is carried out by providing a clearance between the screen plate and a printing surface of a material to be printed, coating a paste-state or ink-state coating material on the surface of the screen plate by a scraper, and then printing the paste-state or ink-state coating material coated on the surface of the screen plate to a material to be printed by a squeegee.
Also, in the screen printing by a stencil using a stencil made of a metal, bubbles are accumulated at the bottom portion of the pore portions of the stencil, so that resin encapsulation of electronic parts cannot be carried out when the electronic parts are required to have high quality and high performances. Thus, for example, in Japanese Laid-Open Patent Application No. 2000-216526, it is disclosed that the above problem can be prevented by performing the resin encapsulation under vacuum atmosphere. Also, in Japanese Laid-Open Patent Application No. Hei 10-313015, it is disclosed to separately carry out feeding of a resinous solution under atmospheric pressure conditions and stencil printing under vacuum atmosphere.
However, in the conventional screen printing method, the ink in an ink fountain is thick and thus bubbles are difficult to remove. Moreover, rolling is carried out by pushing the ink fountain portion, so that ink containing bubbles is transferred. Also, in the screen printing method using a stencil under vacuum atmosphere, bubbles are removed from the surface of the resin encapsulated portion provided by printing when it is returned to atmospheric pressure from vacuum atmosphere, so that unevenness occurs on the surface of the printed surface by the popped bubbles. The positions or sizes of the popped bubbles cannot be expected and controlled so that there is a fear of causing significant gaps in an amount or thickness of the paste-state or ink-state coating material to be printed.
Also, when a stencil contacts the printing surface of a material to be printed and printing is carried out such that a paste-state or ink-state coating material flows into a pore portion of the stencil, a stencil and a material to be printed are incompletely adhered. Thus, a coating material migrates from the pore portion of the stencil to the back surface side thereof so that there is a possibility of adhering a coating material to an unintentional portion of the surface of the material to be coated.
Moreover, in a screen printing method using a screen plate comprising a gauze adhered plate, when printing is carried out on a material to be printed by coating a paste-state or ink-state coating material on the surface of the screen plate by a scraper, and then a paste fountain or ink fountain stand is applied at one end side of the surface of the screen plate by a squeegee, excessive coating material is printed to the material to be printed by the screen plate. Thus, there is a fear of attaching the coating material to a portion of the material to be printed other than that portion desired to be printed, or oozing occurring.
An object of the present invention is to provide a screen printing method which can degas a paste-ink or ink-state coating material before printing, can prevent unevenness of the surface of a printed surface due to bubbles popped from the surface of a printed resin encapsulated portion, can carry out screen printing of high-quality and high-performance electronic parts by providing an amount or thickness of a paste-state or ink-state coating material to be printed, can avoid attaching a coating material to an unintentional portion of the surface of a material to be printed, and can avoid printing excessive printing material to the material to be printed from a screen plate, attaching a coating material to a portion other than a desired portion of the material to be printed, or causing oozing.
To accomplish the above-mentioned objects, a screen printing method of the first embodiment of the present invention comprises placing a material to be printed at a predetermined portion of a printing table, feeding a paste-state or ink-state coating material to a surface of a screen plate for printing, and sliding the surface of the screen plate relative to the surface of a squeegee to carry out screen printing.
The above-mentioned paste-state or ink-state coating material is covered on the surface of the screen plate for printing with a thin thickness, and the paste-state or ink-state coating material coated on the surface of the screen plate for printing is printed to a material to be printed by the above-mentioned squeegee under vacuum or atmospheric pressure. After the above-mentioned coating step, a degassing step is performed to degas bubbles in the coated material by changing the pressure from a high vacuum state to atmospheric pressure or a low vacuum state.
Also, the screen printing method of the second embodiment of the present invention comprises placing a material to be printed at a predetermined portion of a printing table, feeding a paste-state or ink-state coating material to a surface of a screen plate for printing, and sliding the surface of the screen plate relative to the surface of a squeegee to carry out screen printing.
The above-mentioned paste-state or ink-state coating material is covered on the surface of the screen plate for printing with a thin thickness, and the paste-state or ink-state coating material coated on the surface of the screen plate for printing, which is obtained from an ink fountain at a side of one edge of the surface of the screen plate, is printed by the above-mentioned squeegee in vacuum or atmospheric pressure.
Also, the screen printing method of the third embodiment of the present invention comprises placing a material to be printed at a predetermined portion of a printing table, feeding a paste-state or ink-state coating material to a surface of a screen plate for printing, and sliding the surface of the screen plate relative to the surface of a squeegee to carry out screen printing.
The above-mentioned paste-state or ink-state coating material is covered on the surface of the screen plate for printing with a thin thickness, and the paste-state or ink-state coating material coated on the surface of the screen plate for printing, which is obtained from an ink fountain at a side of one edge of the surface of the screen plate, is printed by the above-mentioned squeegee in a vacuum or atmospheric pressure. After the above-mentioned coating step, a degassing step is performed to degas bubbles in the coated material by changing the pressure from a high vacuum state to atmospheric pressure or a low vacuum state.
Also, the screen printing method of the fourth embodiment of the present invention comprises placing a material to be printed at a predetermined portion of a printing table, feeding a paste-state or ink-state coating material to a surface of a screen plate for printing, and sliding the surface of the screen plate relative to the surface of a squeegee to carry out screen printing.
The above-mentioned paste-state or ink-state coating material is covered on the surface of the screen plate for printing with a thin thickness, and the paste-state or ink-state coating material coated on the surface of the screen plate for printing, which is obtained from an ink fountain at a side of one edge of the surface of the screen plate in the coating step, is printed by the above-mentioned squeegee in a vacuum or atmospheric pressure. After completion of the above-mentioned coating step and before the printing step, a degassing step is performed to degas bubbles in the coated material by changing the pressure from a high vacuum state to atmospheric pressure or a low vacuum state, and the printing step is carried out in a vacuum atmosphere.
Also, the screen printing method of the fifth embodiment of the present invention comprises covering a paste-state or ink-state coating material on the surface of a screen plate for printing with a thin thickness by a scraper a plural number of times. A height of the scraper at the latter coating is made the same or different as the height of the scraper at the former coating.
Also, in the screen printing method of the sixth embodiment of the present invention, the above-mentioned screen plate for printing is a gauze-adhered plate or stencil.